Research suggests that military service influences the policy preferences of political elites. Yet, these studies have not considered how self-selection into the armed forces may affect these results. I employ vulnerability to the Vietnam draft lottery to consider two mechanisms for the influence of military service on policy preferences: self-selection and socialization. I compare the roll call votes of Members of Congress in the House of Representatives across the 94th to 113th Congresses who were eligible for the draft and served in the military to those who were eligible for the draft but did not serve. I find a significant difference in the roll call voting behavior between these two groups on foreign and defense policy issues. This distinction cannot be explained by self-selection effects alone, indicating military service is transformative and carrying implications for the study of civil-military relations and elite decision-making in international security.